Met today’s protein target? Research suggests less may help you live longer

What is the logic for dialling back protein, and how should it be read in the face of advice to the contrary? We explain.

The case against high-protein diets

The American researchers, many of whom are affiliated with the University of Wisconsin-Madison, detail the concept of a low-protein diet. It has its origins in a 1935 research study by Cornell University scientists, where biochemist Clive M McCay found that Calorie Restriction (CR), or a low-calorie diet, extends the lifespan of rats.

Whether it was entirely replicable for humans was questionable, also due to the difficulties in maintaining a CR diet. Still, it found that, “In rodents, the ratio of dietary macronutrients profoundly impacts lifespan, with low-protein, high-carbohydrate diets extending lifespan and improving metabolic health.”

A low-protein diet, also referred to as protein restriction (PR), derives from this idea. It is “a robust geroprotective regimen that lowers total dietary protein intake while still meeting nutritional needs. Like CR, PR improves healthspan and increases the lifespan of yeast, flies, and rodents,” the article said.

Several factors are likely behind this connection. According to the article, a primary mediator of the metabolic benefits of PR is fibroblast growth factor 21 (FGF21), a hormone induced by nutritional stress, including fasting. “Dietary PR robustly elevates FGF21 in mice, rats, and humans. Multiple groups have shown that FGF21 is required for many metabolic effects of PR,” it said.

A leading hypothesis for the geroprotective (linked to slowing down aging) effects of PR is “altered nutrient pathway signaling”. It means that a situation of scarcity promotes catabolic pathways, or the breakdown of bigger molecules into smaller ones, with release of energy. It also induces autophagy, the process through which damaged cells are repaired or discarded. “Molecular analysis of aging rate indicators shows that PR shifts the molecular signature of the liver toward a more youthful state,” the article said.

Another area of interest is amino acids, which are the molecules that combine to form proteins. However, certain kinds of amino acids, when consumed in excessive quantities, can contribute to obesity, insulin resistance, and mortality in humans.

The pro-protein view

The article acknowledged that a PR diet can go against official guidelines for existing nutritional requirements. For example, the Dietary Guidelines for America suggest 1.2–1.6 g protein/kg of body weight.

Dudley Lamming, the paper’s corresponding author at the University of Wisconsin-Madison, told ScienceDaily, “But because most people are relatively sedentary, many people are likely consuming more protein than they actually need, which probably has negative health consequences.”

“Seemingly contradictory studies leave many wondering what the optimal amount of dietary protein is for healthy aging. A 2025 report found that 61% of American consumers increased their protein intake in 2024, up from 48% in 2019, suggesting that many Americans believe that higher protein intake is beneficial,” the article said.

At the same time, it does not uniformly advocate for PR diets. It pointed out gaps in what is known about the optimal levels of protein intake, and the potential for variations. Groups such as pregnant women, growing children, and those recovering from injuries may need a high-protein diet, it said.

“While challenges remain in determining the optimal levels of dietary protein and specific amino acids for individual health, the potential benefits of doing so are great enough that they demand that scientists take the necessary next steps to translate these interventions into therapies for humans,” it said. Ultimately, it called for clinical researchers to work together and design suitable diets for individuals; identify methods and metrics to assess the effects of diet on health, frailty, and aging; and understand how personal factors impact dietary needs.

The review indicates that the debate over protein is far from over. If anything, it reiterates the need to further study the building blocks of the human body, at a time when broader messaging is almost uniformly encouraging a certain type of consumption.